To ensure that laying hens can make full use of the various resources within an aviary barn and develop optimum bone health while minimizing keel bone fractures, appropriate cognitive and bone development during rearing is critical. Given previous work documenting the benefit of ramps that could be used by hens to transition between tiers and reduced incidence of keel bone fractures, the project examined the provision of ramps during the rearing period, which birds could use voluntarily from 10 d of age. We hypothesized that the provision of ramps would influence how pullets distribute within the aviary and how birds vertically move between the aviary tiers leading to greater bone strength in birds with access to ramps. The study used 2 flocks of laying hen chicks (Lohmann Selected Leghorn; 4,800 chicks/flock) that were reared in one of 2 commercial rearing facilities with each divided into 4 pens (600 chicks/pen) to allow for treatment assignments. In 2 pens of each facility, ramps were installed from each of the 3 tiers providing a walking path that birds could access from 10 d of age. Video recordings were made at 4 times per day at 3, 4, 5, 8, 11, and 14 wk of age to determine the relative distribution of birds and the number of transitions between each tier. At 16 wk of age, 10 birds per pen per flock were killed and the tibia and humerus collected for biomechanical assessment; the keel was also collected for bone mineral density via computed tomography. Chicks/pullets within pens provided ramps demonstrated a rapid use of the upper tiers of the aviary paralleling greater usage of ramps between all aviary levels. Despite the ramp and tier usage following the predicted pattern, differences in bone strength were opposite than expected for tibiae and may reflect the different behaviors pens with ramps and without ramps would allow. Results support the position that provision of ramps within a commercial system will lead to voluntary usage of the ramps with long term effects on the distribution of birds in the system throughout the rearing period.
